Abstract

We have developed a femtosecond magneto-optical imaging system that allows measurements of permanent magnetic effects that are initiated by a single excitation pulse. The system combines a subpicosecond temporal resolution and a high spatial resolution. We demonstrate the system in an experiment that studies the laser-induced magnetization reversal in ferromagnetic thin films.

(a) Pump–probe measurements at different time delays, at zero field and at H0, with a pump fluence of 48mJ∕cm2. Permanent reversal is obtained only at H0 (in these measurements an ≈0.2cm diameter iris was used, yielding a resolution of ≈50μm); (b) slow measurements carried out in the timed exposure configuration. The elapsed times from the moment of excitation by a single pump pulse are indicated. Spontaneous reversal can be seen on the right of the images.

Nonlocal effects of a single pump pulse at H0. (a) is a reference measurement without pump excitation. (b) and (c) show the effects of excitation in soft and hard parts of the sample, respectively. In (b) the reversal quickly spreads out of the excitation spot. In (c) the pattern of the domain wall movement is affected (compare to Fig. 2): the spontaneous reversal spreads toward the pump-induced reversal but is delayed in the area at the top of the images (indicated by a circle). The elapsed times from the moment of excitation are indicated.